Composting is a process of converting organic and other waste materials into a useful or more valuable commodity. A common application of composting is the aerobic decomposition of waste products from animals, plants or other organic material, resulting in fertilizer ingredients and other soil conditioners. Waste treatment plants also commonly employ composting to treat sewage sludge, often by mixing additional ingredients to facilitate the process. Landfills also may compost various materials. Remediation of contaminated soils is a process to clear the soil of unwanted contaminants and requires mixing and aerating the soil.
Regardless of the application, composting generally requires the availability of oxygen for the aerobic decomposition process. Where the material is not exposed to oxygen, or is exposed to insufficient amounts of oxygen, the decomposition process does not proceed or becomes much less efficient. In smaller scale operations, such as a backyard garden, one may expose the waste material to oxygen by periodically mixing it and exposing it to the surrounding air. In larger scale operations, the process of mixing and aerating the waste material becomes more problematic.
In a commercial or other large scale operation, the material desired to be composted typically is positioned into long rows of generally conically-shaped piles, referred to as windrows, that are relatively consistent in width and in maximum height. The windrows may be constructed by positioning the material into rows on a field by dump trucks, front end loaders, conveyors or other moving equipment. If the material is simply left undisturbed in these windrows, the aerobic decomposition may proceed satisfactorily in some parts of the windrow, but would not do so uniformly within the windrows. The larger the windrow, the greater the amount of material that rests in pockets that are not adequately exposed to oxygen.
In addition to the need to mix and aerate the material itself, one may wish to mix into the windrow additional materials to aid in the decomposition process or to create a desired end product. For example, if treating sewage sludge with a relatively high concentration of nitrogen, one may wish to add other materials, such as wood chips. Similarly, remediation of contaminated soils may advantageously mix certain materials into the windrow to enhance the process.
To enhance aerobic decomposition and soil remediation, a compost turner may be used to mix and aerate the materials. A compost turner is a portable machine designed to travel over a windrow of a certain width and height and, using a rotating horizontal drum with blades or other edges, mix the material in the windrow and expose more of the material to the surrounding air. For the composting and remediation processes to proceed most efficiently, the material should be regularly and thoroughly mixed and aerated by the compost turner.
For commercial or other large scale composting or remediation operations, the windrow may be as small as a few feet high and several feet wide, or may be much larger. As the width and height of the windrow increases, the horsepower requirements of the compost tuner increase significantly. For example, in a relatively smaller commercial windrow having a maximum height of about approximately 5 feet high and a maximum width of approximately 14 feet, the compost turner may require an engine of approximately 250 to 300 horsepower to adequately mix and aerate the material in the windrow. In contrast, a larger windrow of 6 feet high and 20 feet wide may require a compost turner with an engine having 350 to 600 horsepower or more. With compost turners of higher horsepower, e.g., approximately 350 to 600 horsepower or more, the limiting operating factor becomes the ability of the drive assembly to reliably transfer the engine's power to the drum, at an amount of torque and revolutions per minute that will satisfactorily turn the rotating drum.
As the capacity of the compost turner increases, the rotating drum generally increases in size and weight. For a relatively larger compost turners, the drum may reach 5,000 to 6,000 pounds or more. This adds to the forces on the drive system, particularly when the drum shaft is first engaged. A typical clutch mechanism generally is insufficient to reliably engage such a heavy drum over time.
Due to the relatively high horsepower requirements of commercial and other large scale composting, most current self-propelled compost turners employ a hydraulic drive, rather than a clutch mechanism, to engage the drive shaft. However, hydraulic drives are relatively inefficient in transferring horsepower from the engine to a shaft. For example, in these applications, hydraulic drives typically lose at least 15% and perhaps up to 25–30% of available horsepower. Also, hydraulic drives generate a significant amount of heat, which must be dissipated. This mechanism also is relatively complicated, resulting in relatively more frequent and expensive maintenance and replacement.
Another approach is to use a fluid coupler, which advantageously is capable of relatively slowly starting a high inertia load, such as a large drum of a higher capacity compost turner. Fluid couplers are generally very efficient and also are better able to handle a shock load. For example, if the rotating drum of a compost turner were to strike an immoveable object, a fluid coupler may allow the drum to slow or even stop rotating, without stopping the engine.
To power the rotating horizontal drum of the compost turner, typically the engine is used to rotate a drive shaft, which eventually is used to rotate a drum shaft which rotates the drum. A variety of mechanisms may be used to transfer the power from the rotating drive shaft to the drum shaft. One type of mechanism is a belt and pulley system, which typically employs a V-belt connected to a pulley having a V-grooved surface. These types of belt are susceptible to a relatively large amount of stretching, which leads to slippage and inefficient power transfer. As such, they must be tightened periodically and significantly. Also, the alignment of these belts must be within close parameters and closely monitored, to reduce the tendency of the belts to ride off the pulley.
This type of belt and pulley system for reduction generally is better equipped for relatively lower horsepower applications with higher revolutions per minute, such as those having less than approximately 300 horsepower or so. As the horsepower of the compost turner increases and the drum revolutions per minute decreases, higher torque is achieved and the V-belts must be increased in width and/or in number to handle the increased loads. For example, for a compost turner having an engine generating approximately 350 horsepower, such a belt and pulley system may require a V-belt, or a combination of V-belts, to have a width of about 12 inches or greater. This results in greater likelihood of slippage and misalignment, more difficulties in tightening and alignment, decreased efficiency, increased size of the assembly and other design problems resulting from a larger pulley system to handle the width and/or number of belts. For example, the sheer width of the V-belt and pulley system can create a relatively long overhang on a shaft, which places greater pressure on associated bearings and other support structure. At about 350 horsepower or greater and at lower revolutions per minute, the resulting higher torque typically will cause V-belt drive systems to fail.
To address the shortcomings of the V-belt and pulley system, a synchronous poly belt and related pulley system has been employed. A synchronous poly belt generally includes a sequence of rows of teeth and grooves designed to engage corresponding rows of grooves and teeth on the pulleys. The poly belts are typically made of polymers and are stronger and less susceptible to stretching than V-belts. As such, poly belts generally are capable of handling greater horsepower at lower revolutions per minute than V-belts. Also, the engagement of the teeth and groves between the poly belt and the pulleys results in no slippage, less horsepower loss and overall a more efficient power transfer.
Whether using a V-belt or a poly belt system, the horsepower generated by the engine must be transferred to start and maintain the rotation of the drum of the compost turner. To do so, it is advantageous to conduct a reduction, i.e., reduce the revolutions per minute and increase the torque, in order to overcome the inertia of the drum and rotate the drum at the desired, lower revolutions per minute. In theory, this may be accomplished in a single step, with a drive shaft connected by the pulley and belt system directly to a drum shaft. In applications such as the compost turners described herein, a single step reduction would place inordinate stress on the drive assembly and require unacceptably large and unwieldy components. As such, a two step reduction process may be employed, where the drive shaft is connected by the poly belt and pulley system to a jack shaft, which in turn is connected by a second poly belt and pulley system to the drum shaft.
Generally, a jack shaft rotates around a bearing assembly, which is connected to a portion of the frame of the compost turner. With a pulley at one end of the jack shaft connected by a belt to a pulley on the drive shaft, the jack shaft and the bearing assembly are subjected to forces in the direction of the drive shaft when the drive shaft is engaged. As the amount of horsepower increases, the forces on the jack shaft and the bearing assembly increase correspondingly. Also, the jack shaft includes a pulley connected by a belt to a pulley on the drum shaft. This results in forces on the jack shaft and bearing assembly in the direction of the drum shaft, when the drive shaft is engaged. For compost turners of relatively larger capacity, e.g., those with horsepower of approximately 350 or greater, these forces are relatively large and are difficult for existing jack shaft and bearing assembly systems to handle.
One approach for such larger capacity compost turners has been to place one or more bearing assemblies near the middle of the jack shaft, with the pulley to the drive shaft on one side and the pulley(s) to the drum shaft on the other. While this approach may be suitable for many applications, it is less reliable and durable than desired for commercial and other large scale composting operations. That is, a single bearing assembly, or even a pair of bearing assemblies, positioned between the pulley to the drive shaft and the pulley(s) to the drum shaft have been found to be insufficient to handle the loads imposed by such larger capacity compost turners, such as those having approximately 350 horsepower or greater.
As such, a need exists for an improved reduction assembly for a compost turner or other equipment operating at relatively higher horsepower and requiring reduction resulting in lower revolutions per minute and greater torque, e.g., to start and maintain the rotation of the revolving drum of a commercial compost turner.